Blood pressure is the net result of stroke volume and vascular resistance or impedance. Blood pressure can increase with an increase in stroke volume as occurs with exercise or with adrenaline. Blood pressure can also increase with an increase in arterial tone, which is the usual cause of essential hypertension. Blood pressure increases with vasoconstrictors such as phenylephrine or angiotensin which raise blood pressure solely by increasing vascular stiffness.
It would be very useful to be able to quantify the relative contribution of stroke volume and arterial stiffness to blood pressure. For example, if the oscillometrically measured blood pressure is 150/80, are these high numbers due to increases in stroke volume or from arterial stiffness? The decision to treat or not to treat, and/or the determination of what agent to use, could vary, depending upon the result.
Similarly, the response to the treatment to be followed can vary with the result. For example, if a vasodilator such as an angiotensin receptor blocker (ARB) is used, the change in vascular stiffness may be more important to follow, rather than blood pressure alone, as arterial stiffness is the primary pathology.
In the acute care setting, a non-invasive measure would help in decision-making to diagnose and manage heart failure or sepsis with vasoactive drugs and fluid.
There is also a large group of people with normal blood pressure but increased vascular stiffness. A non-invasive way of assessing the degree of vasoconstriction and cardiac performance would be helpful in diagnosing and treating such patients. Other patients have unrecognized vascular stiffness yet their blood pressure does not reach the 140/90 threshold of treatment. How to treat (or not to treat) these patients is unclear. The ability to further characterize those patients who may have so-called “pre-hypertension” into those with and without vascular stiffness could provide a way forward in therapy and prevention of premature vascular death.
Increasingly, there is evidence that the central, aortic blood pressure and flow waveforms contain information that can help to answer the questions above. However, the indices commonly derived from the pressure waveform are based on apparent morphology, rather than the underlying physics, there are difficulties in accurately estimating the central pressure waveform morphology from a non-invasive measurement, and it is difficult to measure the aortic flow waveform in a non-invasive manner. This invention addresses all of these issues.